This invention relates in general to a seam treatment process and, more specifically, to a stress release and protrusions elimination process for seams of flexible belts.
Flexible electrostatographic belt imaging members are well known in the art. Typical electrostatographic flexible belt imaging members include, for example, photoreceptors for electrophotographic imaging systems, electroreceptors such as ionographic imaging members for electrographic imaging systems, and intermediate transfer belts for transferring toner images in electrophotographic and electrographic imaging systems. These belts are usually formed by cutting a rectangular sheet from a web containing at least one layer of thermoplastic polymeric material, overlapping opposite ends of the sheet, and joining the overlapped ends together to form a welded seam. The seam extends from one edge of the belt to the opposite edge. Generally, these belts comprise at least a supporting substrate layer and at least one imaging layer comprising thermoplastic polymeric matrix material. The xe2x80x9cimaging layerxe2x80x9d as employed herein is defined as the dielectric imaging layer of an electroreceptor belt, the transfer layer of an intermediate transfer belt and, the charge transport layer of an electrophotographic belt. Thus, the thermoplastic polymeric matrix material in the imaging layer is located in the upper portion of a cross section of an electrostatographic imaging member belt, the substrate layer being in the lower portion of the cross section of the electrostatographic imaging member belt. Although the flexible belts of interest consist of these mentioned types, nonetheless for simplicity reason, the discussion hereinafter will be focused only on the electrophotographic imaging member belts.
Flexible electrophotographic imaging member belts are usually multilayered photoreceptors that comprise a substrate, an electrically conductive layer, an optional hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer and, in some embodiments, an anti-curl backing layer. One type of multilayered photoreceptor comprises a layer of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. A typical layered photoreceptor having separate charge generating (photogenerating) and charge transport layers is described in U.S. Pat. No. 4,265,990, the entire disclosure thereof being incorporated herein by reference. The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer.
Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers were developed, fatigue induced cracking of the charge transport layer at the welded seam area is frequently encountered during photoreceptor belt cycling. Moreover, the onset of seam cracking has also been found to rapidly lead to seam delamination due to fatigue thereby shortening belt service life. Dynamic fatigue seam cracking and delamination also occurs in ionographic imaging member belts and may possibly happen in intermediate transfer belts as well.
The flexible electrophotographic imaging member belts are fabricated from sheets cut from a web. The sheets are generally rectangular in shape. All edges may be of the same length or one pair of parallel edges may be longer than the other pair of parallel edges. The sheets are formed into a belt by joining overlapping opposite marginal end regions of the sheet. A seam is typically produced in the overlapping marginal end regions at the point of joining. Joining may be effected by any suitable means. Typical joining techniques include welding (including ultrasonic), gluing, taping, pressure heat fusing, and the like. Ultrasonic welding is generally the preferred method of joining because is rapid, clean (no solvents) and produces a thin and narrow seam. In addition, ultrasonic welding is preferred because the mechanical pounding of the welding horn causes generation of heat at the contiguous overlapping end marginal regions of the sheet to maximize melting of one or more layers therein. A typical ultrasonic welding process is carried out by holding down the overlapped ends of a flexible sheet with vacuum over a flat anvil and guiding the flat end of an ultrasonic vibrating horn transversely across the width of the sheet and along the length of the overlapped ends to form a welded seam.
When ultrasonically welded into a belt, the seam of multilayered imaging flexible members may occasionally contain undesirable high protrusions such as peaks, ridges and mounds. These seam protrusions present problems during image cycling of the belt machine because they interact with cleaning blades to cause blade wear and tear which ultimately affect cleaning blade life and efficiency. Moreover, the high protrusions in the seam may also interfere with the operation of subsystems of copiers, printers and duplicators by damaging electrode wires used in development subsystems that position the wires parallel to and closely spaced from the outer imaging surface of belt photoreceptors. These closely spaced wires are employed to facilitate the formation of a toner powder cloud at a development zone adjacent to a toner donor roll and the imaging surface of the belt photoreceptor. Another frequently observed mechanical failure in imaging belts during image cycling is that the ultrasonically welded seam of an electrophotographic imaging member belt can also develop cracks which then propagate into delamination after being subjected to extended fatigue bending and flexing cycles over small diameter belt support rollers of an imaging machine or when due to lateral forces caused by mechanical rubbing contact with stationary web edge guides of a belt support module during cycling. Seam cracking/delamination has also been found to be further aggravated when the belt is employed in electrophotographic imaging systems utilizing blade cleaning devices. Alteration of materials in the various photoreceptor belt layers such as the conductive layer, hole blocking layer, adhesive layer, charge generating layer, and/or charge transport layer to suppress cracking and delamination problems is not easily accomplished. The alteration of the materials may adversely affect the overall electrical, mechanical and other properties of the belt such as well as residual voltage, background, dark decay, flexibility, and the like.
For example, when a flexible imaging member belt used in an electrophotographic machine is a photoreceptor belt fabricated by ultrasonic welding of overlapped opposite ends of a sheet, the ultrasonic energy transmitted to the overlapped ends melts the thermoplastic sheet components in the overlap region to form a seam. The ultrasonic welded seam of a multilayered photoreceptor belt is relatively brittle and low in strength and toughness. The joining techniques, particularly the welding process, can result in the formation of a splashing that projects out from either side of the seam in the overlap region of the belt. The overlap region and the spashings on each side of the overlap region comprise a strip from one edge of the belt to the other that is referred herein as the xe2x80x9cseam regionxe2x80x9d. Because of the splashing, a typical flexible imaging member belt is about 1.6 times thicker in the seam region than that of the remainder of the belt (e.g., in a typical example, 188 micrometers versus 1.6 micrometers).
The photoreceptor belt in an electrophotographic imaging apparatus undergoes bending strain as the belt is cycled over a plurality of support and drive rollers. The excessive thickness of the photoreceptor belt in the seam region due to the presence of the splashing results in a large induced bending strain as the seam travels over each roller. Generally, small diameter support rollers are highly desirable for simple, reliable copy paper stripping systems in electrophotographic imaging apparatus utilizing a photoreceptor belt system operating in a very confined space. Unfortunately, small diameter rollers, e.g., less than about 0.75 inch (19 millimeters) in diameter, raise the threshold of mechanical performance criteria to such a high level that photoreceptor belt seam failure can become unacceptable for multilayered belt photoreceptors. For example, when bending over a 19 millimeter diameter roller, a typical photoreceptor belt seam splashing may develop a 0.96 percent tensile strain due to bending. This is 1.63 times greater than a 0.59 percent induced bending strain that develops within the rest of the photoreceptor belt. Therefore, the 0.96 percent tensile strain in the seam splashing region of the belt represents a 63 percent increase in stress placed upon the seam splashing region of the belt.
Under dynamic fatiguing conditions, the seam provides a focal point for stress concentration and becomes the point of crack initiation which is further developed into seam delamation causing premature mechanical failure in the belt. Thus, the splashing tends to shorten the mechanical life of the seam and service life of the flexible member belts used in copiers, duplicators, and printers.
Although a solution to suppress the seam cracking/delamination problem has been successfully demonstrated, as described in a prior art, by a specific heat treatment process of a flexible electrophotographic imaging member belt with its seam parked directly on top of a 19 mm diameter back support rod for stress-releasing treatment at a temperature slightly above the glass transition temperature (Tg) of the charge transport layer of the imaging member, nevertheless this seam stress release process was also found to produce various undesirable effects such as causing seam area imaging member set and development of belt ripples in the active electrophotographic imaging zones of the belt (e.g., the region beyond about 25.2 millimeters from either side from the midpoint of the seam). Moreover, the heat treatment can induce undesirable circumferential shrinkage of the imaging belt. The set in the seam area of an imaging member mechanically adversely interacts with the cleaning blade and impacts cleaning efficiency. The ripples in the imaging member belt manifest themselves as copy printout defects. Further, the heat induced imaging belt dimensional shrinkage alters the precise dimensional specifications required for the belt. Another key shortcoming associated with the prior art seam stress release heat treatment process is the extensive heat exposure of a large seam area. This extensive heat exposure heats both the seam area of the belt as well as the rod supporting the seam. Since the belt must be cooled to below the glass transition temperature of the thermoplastic material in the belt prior to removal from the support rod in order to produce the desired degree of seam stress release in each belt, the heat treatment and cooling cycle time is unduly long and leads to very high belt production costs.
Since there is no effective way to prevent the generation of localized high protrusions at the seam, imaging member belts are inspected, right after the seam welding belt production process, manually by hand wearing a cotton glove through passing the index finger over the entire seam length, and belts found catching the glove by the protrusion spots are identified as production rejects. Both the time consuming procedure of manual inspection and the number of seamed belts rejected due to the presence of high seam protrusions constitute a substantial financial burden on the production cost of imaging member belts.
Therefore, there is an urgent need for improving the physical quality and mechanical performance of seamed flexible imaging member belts having seams that are free of protrusions and which can withstand greater dynamic fatigue conditions to thereby extending belt service life. It is also important, from the imaging member belt production point of view, that effective cutting of unit manufacturing cost of a seamed imaging belts can be realized if an innovative post seaming treatment process can be developed to provide the dual function of effecting seam stress release and eliminating seam protrusions in a single process. With this innovative post seaming treatment process, the need for a manual seam inspection procedure is eliminated because the process can effectively remove seam protrusions from those imaging member belts that are otherwise lost as rejects.
U.S. Pat. No. 5,240,532, issued to Yu on Aug. 31, 1993xe2x80x94A process for treating a flexible electrostatographic imaging web is disclosed including providing a flexible base layer and a layer including a thermoplastic polymer matrix comprising forming at least a segment of the web into an arc having a radius of curvature between about 10 millimeters and about 25 millimeters measured along the inwardly facing exposed surface of the base layer, the arc having an imaginary axis which traversed the width of the web, heating at least the polymer matrix in the segment to at least the glass transition temperature of the polymer matrix, and cooling the imaging member to a temperature below the glass transition temperature of the polymer matrix while maintaining the segment of the web in the shape of the arc.
U.S. Pat. No. 5,552,005 to Mammino et al., issued Sep. 3, 1996xe2x80x94A flexible imaging sheet and a method of constructing a flexible imaging sheet is disclosed. The method of constructing a flexible imaging sheet comprises a step of overlapping, a step of joining, and a step of shaping. In the step of overlapping, a first marginal end region and a second marginal end region of a sheet are overlapped to form an overlap region and a ex non-overlap region. In the step of joining, the first marginal end region and the second marginal end region of the sheet are joined to one another by a seam in the overlap region. In the step of shaping, the overlap region is shaped to form a generally planar surface co-planar with a surface of the non-overlap region. The flexible imaging sheet comprises a first marginal end region and a second marginal end region. The first marginal end region and the second marginal end region are secured by a seam to one another in the overlap region. The first marginal end region and the second marginal end region are substantially co-planar to minimize stress on the flexible imaging sheet. Minimization of stress concentration, resulting from dynamic bending of the flexible imaging sheet during cycling over a roller within an electrophotographic imaging apparatus, is particularly accomplished in the present invention.
U.S. Pat. No. 5,376,491 to Krumberg et al., issued Dec. 27, 1994xe2x80x94An organic photoconductor is disclosed including a base layer formed of a first material and a photoconductive layer formed of a second material. The organic photoconductor being characterized in that when it is maintained in a curved orientation with the photoconductive layer facing outward, the photoconductive layer is subjected to less stress than the base layer. In one embodiment the first material is relatively more flexible and stretchable than said second material and the materials are pre-stressed in opposite senses. In a second embodiment the first material is relatively flexible and stretchable and the second material is an initially less flexible and stretchable material which has been chemically treated to increase its stretchability and flexibility.
U.S. Pat. No. 5,021,109 to Petropoulous et al., issued Jun. 4, 1991xe2x80x94A process is disclosed for preparing a multilayered belt comprising the steps of: (1) heating a substrate in a form of a tubular sleeve and formed of a polymeric material to at least about a glass transition temperature of the polymeric material, so as to expand the tubular sleeve; (2) placing the expanded tubular sleeve on a mandrel; (3) treating the tubular sleeve by applying one or more multilayered composite belts; (4) layers on the sleeve to form a heating composite belt to at least about the glass transition temperature of the polymeric material of the tubular sleeve; and (5) cooling the composite belt.
U.S. Pat. No. 5,603,790 to Rhodes, issued Feb. 18, 1997xe2x80x94Process and apparatus for fabricating belts are disclosed. The process includes conveying the leading edge of a flexible web from a supply roll past a slitting station, slitting the web a predetermined distance from the leading edge to form a web segment having the leading edge at one end and a trailing edge at the opposite end, maintaining the web slack at the location where the web is slit during slitting, overlapping the leading edge and the trailing edge of the web segment to form a joint and welding the joint to permanently join the leading edge and the trailing edge together to form a belt. The apparatus includes means to convey the leading edge of a flexible web from a supply roll past a slitting station, means at the slitting station to slit the web a predetermined distance from the leading edge to form a web segment having the leading edge at one end and a trailing edge at the opposite end, means to maintain the web slack at the location where the web is slit during slitting, means to overlap the leading edge and the trailing edge of the web segment to form a joint and means to weld the joint to permanently join the leading edge and the trailing edge together to form a belt.
U.S. Pat. No. 4,840,873 to Kobayashi et al., issued Jun. 20, 1989xe2x80x94A process is disclosed for producing an optical recording medium comprising the step of heat treating an optical recording medium comprising a plastic substrate having a surface of minutely roughened structure and a thin metal film formed on the surface. The optical recording medium is heated at a temperature within a range which is lower by 80xc2x0 C. and higher by 60xc2x0 C. than the glass transition temperature of the plastic substrate.
U.S. Pat. No. 4,532,166 to Thomsen et al., issued Jul. 30, 1985xe2x80x94A welded web is disclosed which is prepared by overlapping a first edge over a second edge, then applying heat necessary to bond the first edge with the second edge. The heating techniques may include ultrasonic welding, radio frequency heating, and the like.
U.S. Pat. No. 3,988,399 to Evans, issued Oct. 26, 1996xe2x80x94Heat recoverable articles are disclosed which have an elongate S-shaped configuration, which later can be wrapped about a substrate. The articles comprise a molecularly oriented unitary polymeric layer which has been differentially annealed while restrained against dimensional change and crosslinking.
This application is related to the following U.S. patent applications:
U.S. patent application Ser. No. 09/004,651, filed on Jan. 8, 1998, in the name of Yu et al., entitled xe2x80x9cDEFOCUSED LASER SEAM STRESS RELEASE IN FLEXIBLE ELECTROSTATOGRAPHIC IMAGING MEMBER BELTSxe2x80x9d, xe2x80x94A process is disclosed for treating a seamed flexible electrostatographic imaging belt including providing an imaging belt having two parallel edges, the belt comprising at least one layer comprising a thermoplastic polymer matrix and a seam extending from one edge of the belt to the other, the seam having an imaginary centerline, providing an elongated support member having at arcuate supporting surface and mass, the arcuate surface having at least a substantially semicircular cross section having a radius of curvature of between about 9.5 millimeters and about 50 millimeters, supporting the seam on the arcuate surface with the region of the belt adjacent each side of the seam conforming to the arcuate supporting surface of the support member, precisely traversing the length of the seam from one edge of the belt to the other with thermal energy radiation having a narrow Gaussian wavelength distribution of between about 10.4 micrometers and about 11.2 micrometers emitted from a carbon dioxide laser, the thermal energy radiation forming spot straddling the seam during traverse, the spot having a width of between about 3 millimeters and about 25 millimeters measured in a direction perpendicular to the imaginary centerline of the seam, and rapidly quenching the seam by thermal conduction of heat from the seam to the mass of the support member to a temperature below the glass transition temperature of the polymer matrix while the region of the belt adjacent each side of the seam conforms to the arcuate supporting surface of the support member. The entire disclosure of this application is incorporated herein by reference.
U.S. patent application Ser. No. 09/004,289, filed on Jan. 8, 1998, in the names of Yu et al., entitled xe2x80x9cSEAM STRESS RELEASE IN FLEXIBLE ELECTROSTATOGRAPHIC IMAGING BELTSxe2x80x9dxe2x80x94A process for treating a seamed flexible electrostatographic imaging belt including providing an imaging belt including at least one layer including a thermoplastic polymer matrix and a seam extending from one edge of the belt to the other, providing an elongated support member having a arcuate supporting surface and mass, the arcuate surface having at least a substantially semicircular cross section having a radius of curvature of between about 9.5 millimeters and about 50 millimeters, supporting the seam on the arcuate surface with the region of the belt adjacent each side of the seam conforming to the arcuate supporting surface of the support member with a wrap angle at least sufficiently enough to provide arcuate support for the seam area, traversing the seam from one edge of the belt to the other with infrared rays from a tungsten halogen quartz bulb focused with a reflector having a hemiellipsoid shape to form a heated substantially circular spot straddling the seam during traverse, the spot having a diameter of between about 3 millimeters and about 25 millimeters, without exceeding the breadth of supported arcuate seam area, to substantially instantaneously heat the thermoplastic polymer matrix in the seam and the region of the belt adjacent each side of the seam directly under the heating spot to at least the glass transition temperature of the polymer matrix without significantly heating the support member, and rapidly quenching the seam by thermal conduction of heat from the seam to the mass of the support member to a temperature below the glass transition temperature of the polymer matrix while the region of the belt adjacent each side of the seam conforms to the arcuate supporting surface of the support member. Apparatus for carrying out this process is also disclosed.
U.S. patent application Ser. No. 09/004,290, filed on Jan. 8, 1998, in the names of Yu et al., entitled xe2x80x9cRAPID ELECTROSTATOGRAPHIC BELT TREATMENT SYSTEMxe2x80x9dxe2x80x94A process is disclosed for treating a seamed flexible electrostatographic imaging belt is disclosed including providing an imaging belt including at least one imaging layer including a thermoplastic polymer matrix and a seam extending from one edge of the belt to the other, the seam having a region on the belt adjacent each side of the seam and also having an exposed surface on each side of the belt, supporting the belt with at least one vacuum holding device spaced from the seam while maintaining the seam and region of the belt adjacent each side of the seam in an arcuate shape having at least a substantially semicircular cross section having a radius of curvature of between about 9.5 millimeters and about 50 millimeters, heating the thermoplastic polymer matrix of the imaging layer in the seam and the region of the belt adjacent each side of the seam to at least the glass transition temperature (Tg) of the thermoplastic polymer matrix without significantly heating the support member, and contacting the exposed surface of the seam and regions on each side of the belt with a gas to rapidly cool the seam and regions on each side of the belt to a temperature below the glass transition temperature of the polymer matrix while maintaining the arcuate shape of the region of the belt adjacent each side of the seam. Apparatus for carrying out this process is also disclosed. The entire disclosure of this application is incorporated herein by reference.
U.S. patent application Ser. No. 09/429,148, filed concurrently herewith, in the names of Yu et al., entitled xe2x80x9cA FLEXIBLE IMAGING BELT SEAM SMOOTHING METHODxe2x80x9dxe2x80x94A process for post treatment of an ultrasonically welded seamed flexible imaging member belt including providing an elongated support member having a smooth flat supporting surface, providing a flexible belt having parallel edges and a welded seam extending from one edge to the other edge, the belt seam including a seam region including an overlap and two adjacent splashings, thermoplastic polymer material having a glass transition temperature and an inner and outer surface, supporting the inner surface of seam on the smooth flat supporting surface with the seam region of the belt held down by vacuum against and conforming to the flat supporting surface of the support member, contacting the seam with a heated surface, the contacting heated surface has a profile that is substantially parallel to the smooth flat supporting surface of the support member, heating the seam region with the heated surface to raise the temperature in the seam region to a temperature of from about 2xc2x0 C. to 20xc2x0 C. above the Tg of the thermoplastic polymer material, and compressing the seam with the heated surface with sufficient compression pressure to smooth out the seam. Apparatus for carrying out the process is also disclosed. The entire disclosure of this application is incorporated herein by reference.
Thus, there is a continuing need for electrostatographic imaging belts having improved resistance to seam cracking and delamination, free of seam protrusions, and free of factors that damage imaging subsystems.
It is, therefore, an object of the present invention to provide an improved electrostatographic imaging member belt which overcomes the above-noted deficiencies.
It is yet another object of the present invention to provide a mechanically robust seamed electrostatographic imaging member belt.
it is still another object of the present invention to provide an improved electrostatographic imaging member belt having an ultrasonically welded seam which exhibits greater resistance to dynamic fatigue induced seam cracking and delamination.
It is another object of the present invention to provide an improved electrostatographic imaging member belt having a welded seam which exhibits greater resistance to cracking and delamination and has no seam area set problem.
It is yet another object of the present invention to provide an improved electrostatographic imaging member belt having a mechanically robust welded seam and exhibiting good circumferential dimension tolerance.
It is also another object of the present invention to provide an improved electrostatographic imaging member belt having a welded seam which is free of induced belt ripples to create copy printout defects.
It is still another object of the present invention to provide a process that yields improved electrostatographic imaging member belts having a welded seam which is free of seam protrusions, exhibits greater resistance to fatigue induced cracking and delamination, has no seam area set, is free of belt ripple development, and maintains good belt dimensional tolerance.
It is still yet another object of the present invention to provide an improved electrostatographic imaging member belt with a stress free state in the imaging layer around the welded seam area when the electrostatographic imaging belt flexes over small diameter support rollers.
The foregoing objects and others are accomplished in accordance with this invention by providing a process comprising
providing a support having an elongated surface with an arcuate convex substantially semicircular cross section having a predetermined radius of curvature,
providing a flexible belt having parallel edges and a welded seam extending from one edge to the other edge, the belt seam comprising a seam region comprising an overlap and two adjacent splashings, polymer material having a glass transition temperature, an inner surface and an outer surface,
supporting the inner surface of the seam on the elongated surface with the belt conforming to the predetermined radius of curvature,
progressively elevating the temperature of localized sites along the seam from one edge of the belt to the other with heat energy to at least the glass transition temperature of the polymer material,
applying line compressive contact against the seam region by pressing a rotatable wheel having a peripheral surface with an arcuate concave cross section having a radius of curvature which matches or is slightly larger than the predetermined curvature of the arcuate convex substantially semicircular cross section of the elongated surface,
simultaneously rolling and pressing a part of the peripheral surface of the rotatable wheel against the outer surface of the seam to continuously generate lines of compressive contact over the seam region from one edge of the belt to the other while the temperature of the localized sites pressed by the wheel is at at least the glass transition temperature of the polymer material, the line of compressive contact at the peripheral surface of the wheel pressing against the outer surface of the seam being
substantially parallel to the predetermined curvature of the elongated surface having an arcuate convex substantially semicircular cross section and
in substantially line contact with the outer surface of the seam, and
rapidly cooling the seam to a temperature below the glass transition temperature of the thermoplastic material while maintaining the belt in conformance with the predetermined arc.
This invention also includes apparatus for achieving stress relaxation and eliminating protrusions in the seam region.
Although this invention relates to apparatus and process improvements for electrostatographic imaging member belts, the following will focus only on electrophotographic imaging belts to simplify discussion.
A more complete understanding of the process and apparatus of the present invention can be obtained by reference to the accompanying drawings wherein: